Berserk is an amazing Manga series. Great story, great characters and it actually does GRIMDARK!!! well. And yeah, Guts is pretty much what a high level fighter in older editions would be like, splattering armies and going up against fairly scary demons. The series is highly recommended, unless gore and at times fairly depressing stuff is a turnoff, in wich case stay the fuck away, seriously. It's made of gore and depressing stuff.

However,
1) the sword is indeed seen as silly and crazy even in-world and is nothing like a zweihander at all and saying it is is extremely o_O
2) I can't see what it's got to do with d&d 5ed unless it goes like
Basic: Pixar style, kid friendly
Advanced: Classic Pre-3e type stuff, aka stuff we like
Extreme!: Blood tits gore gore GORE!!!

...

More on topic, I like the halflings. They actually look like hobbits and d&d halflings haven't in a while. That's a thumbs up from me. And the monsters look cool, well most of them. The rest I'm fairly neutral to, but the art isn't worse than 4e or 3e art, at least, so I suppose I'm cautiously positive.